Port to ROS2

[tonynajjar]

Hey @MichaelGrupp :)

I'd like to use this in ROS2, any interest in porting this to ROS2? I'm happy to help with some guidance from your side

[MichaelGrupp]

Hi Tony, sorry for the late reply. Porting to ROS2 would be nice, however at the moment this would need to be done mainly with external contribution because I don't plan to do this myself in the next time. What I could do is to set up a ros2 branch against which you (or other persons) can create PRs for the port and I can assist in PR reviews.

I cannot help with the implementation details for ROS2 at the moment, but to me the work to be done looks like:

• port pure C++ implementation & test (this should be relatively easy to do I think)
• port Python bindings (here there could be some things that need to be taken care of, e.g. the internal node handle that we have in the ROS1 version)
• port Python tests
• create a CI job including Dockerfile
• adapt README for ROS2

[MichaelGrupp]

Also, in the README we have this here as a motivation for ROS1 explaining why the existing TF2 BufferServer is bad:

The idea is great, but it can scale badly with the number of clients and requests. This is due to the broadcast nature of the ROS action protocol, where each client receives status update callbacks of the currently active goals.

Are ROS2 actions also implemented in such an ugly way? If they are not, this would mean that it would be worth to do some benchmarking of the performance of the TF2 BufferServer in ROS2, maybe it's not so bad anymore?

[tonynajjar]

Sorry for the long wait, we threw back this in the backlog until now.

Are ROS2 actions also implemented in such an ugly way?

I'm not 100% sure of the internals but my observation is that in ROS2 all action clients to a certain server subscribe to the status topic yes.

This PR might interest you ros2/geometry2#573. A service is probably the right way to go long-term, even with this PR but what is the reason you didn't directly go for implementing a service in the existing buffer server as suggested here